1. Field of the Invention
This invention relates to a pneumatic radial tire, and more particularly to a so-called low section pneumatic radial tire having a ratio of tire section height to maximum tire width or an aspect ratio of not more than 0.8.
2. Related Art Statement
Since tread width is relatively wide in this type of the tire, the drainage property that is performance of removing a water layer covering a running road surface from a ground contact area of the tire during the raining is particularly important in order to avoid a dangerous phenomenon such as hydroplaning, aquaplaning or floating when the tire is used on expressways and so on. Therefore, the improvement of tread patterns advantageously satisfying the above requirement is an urgent matter in order to ensure the steering stability of the vehicle under such situations that the tendency of high speed running in passenger cars becomes exceedingly strong and the value of aspect ratio becomes considerably small.
In Japanese Patent laid open No. 57-194,106 (corresponding to U.S. patent application Ser. No 262,238) a tire for racing cars is disclosed wherein the drainage performance and the prevention of tread damage are compromisedly improved through a netted tread pattern formed by arranging circumferential grooves and lateral grooves slantingly crossed therewith over the entire area of the tread portion.
On the contrary, in the low section pneumatic tire for a passenger car, it is required to reduce noise resulting from the rotation of the tire running on roads in addition to the drainage performance as mentioned above. In these noise such as pattern noise, road noise and the like, the sound pressure level rises with the increase of the running speed, resulting in the uncomfortable feeling and hence fatigue to a driver during the high speed running. In this connection, it is very difficult to simultaneously establish the reduction of noises and the drainage performance by the block arrangement based on the above netted tread pattern because the blocks in the netted tread pattern are intermitent on the ground contact area so that clicks are generated at the block end in the treading of the tire and the grooves defining the block cause a column resonance at the ground contact area of the tire.